Re: [PATCH] IBM Lanstreamer bugfixes

[Alan Cox]

> what purpose does the volatile below serve? 
> 
> io.h:122:#define writew(b,addr) (*(volatile unsigned short *) 
> __io_virt(addr) = (b))X
> 
> Is this a sort of "go do this now" command to flush it from the CPU to the 
> PCI bus, while the readw() makes sure its flushed out of the PCI cache? 

The compiler isnt obliged to actually generate the assignment in order
otherwise, so given

	writew(1, foo+2);
	writew(2, foo);

it might have the urge to reverse them - perhaps to optimise in using
postincrement modes

volatile says "stuff happens here beyond the compilers direct knowledge of
events".

Simple example

	i=0;
	while(i<100000) i++;

can be optimised to i=100000 if i is not volatile

Alan